For the first time comprehensive scientific evidence has been gathered about phytoplankton of the northern Black Sea. The study covered the year-long cycle (1992-1993) and eventuated in creation of an original electronic database. 1732 phytoplankton samples have been collected.

Computer programs have been devised to simplity calculation of basic parameters of the phytoplankton. The list of the unicellular microalgae has been compiled and provided with the corresponding figures and formulas for computing volume of the cells. Statistical analysis of the sea which correspond to particular natural oceanological zones has been made. It was found that phytoplankton numbers distributed over the explored areas in conformity with long-normal rule.

For the first time significant relationships (the level of significance £ 0.05) have been disclosed between structural characteristics of phytoplankton and oceanographic parameters in deep-water zone of the Black sea. Significant difference has been elicited between the state of phytoplankton succession (the stability expressed by means of abundance/biomass comparison (ABC index*) in upwellings in comparison with neighbouring waters.

The study has shown the regional features of seasonal and long-term dynamics of diatom to peridinean biomass ratio, and an increase of phytoplankton biomass from the 1970s to the 1980s which proceeded owing to peridineans in the north-west and owing to diatoms in the east of the sea.

It was also found that interannual variability of phytoplankton biomass strongly depends on fluctuations of atmospheric circulation (through the impact on water circulation), the contribution of the atmospheric effect to phytoplankton dispersion was estimated as 56%.

The rise of phytoplankton biomass was fostered by the transfer of air masses generating cyclonic water circulation in the eastern Black Sea and local anticyclonic circulation in the north-western part of the sea.

Another pioneer finding was that in the open Black Sea long-term changes of phytoplankton were determined by superposition of natural (atmospheric circulation) and anthropogenic (irrevocable water-use, i.e. overexploitation of the rivers inflowing into the Black Sea) factors. The results are the loss of phytoplankton biodiversity (by Shannon) and the reduced resistance of the ecosystem to environmental impacts.

* - The index was computed using Meire-Dereu method for comparing abundance and biomass curves (Meire P.M., Dereu J., 1990).